Voltage regulators connected in parallel



Sept. 14, 1937.

W. P. OVERBECK VOLTAGE REGULATORS CONNECTED IN PARALLEL Fflqd Jan. 29, 1935 2 Sheets-Sheet 1 INVENTOR wucox P OVERBECK B Clnwvl ATTORNEY LOAD CURRENT Sept. 1937- w. P; OVERBECK VOLTAGE REGULATORS CONNECTED IN PARALLEL Filed Jan. 29, 1935 2 Sheets-Sheet 2 FIG/.4

INVENTOR WILCOX P OVERBECK BY (9 mm,

ATTORNEY Patented Sept. 14, 1937 UNITED STATES PATENT OFFICE Wilcox P. Over-beck,

to Baytheon Manuf Cambridge, Mala, alllgnor acturlng Company, Newton, Mala, a corporation of Delaware pplication January 29, 1935, Serial No. 3,901

6 Claims. (Cl. 175-383) This invention relates to voltage regulators connected in parallel, and more particularly to such a connection in which the regulators are of the type supplying a rising voltage characteristic to an apparatus such as a rectifier and associated filter, whereby the output voltage of said apparatus is substantially constant.

An object of my invention is to enable a plurality of voltage regulators of the type described to be connected in parallel from a common source of alternating voltage to supply a common load, and automatically cause the load to divide between them in accordance with their power rat- 1 Another object of my invention is to devise such a system in which the load division between the voltage regulators is maintained in a stable manner.

A still further object of my invention is to so enable voltage regulators to be adapted to be connected into such a system with a minimum of additional apparatus.

The foregoing and other objects of my invention will be best understood from the following 25 description of an exemplification thereof, reference being had to the accompanying drawings. wherein:

Fig. 1 is-a diagrammatic representation of one form of my novel system;

30 Fig. 2 is a set of characteristic curves typical of such voltage regulators, as illustrated in Fig. 1;

Fig. 3 is an equivalent circuit diagram of the arrangement shown in Fig. 1; and

Fig. 4 is a vector diagram showing the rela- 35 tionships between the various vector components of the equivalent circuit illustrated in Fig. 3.

It is often desirable in supplying a relatively large load to supply that load from a plurality of voltage regulating devices. To do this it is further desirable to connect said voltage regulators in parallel across a common source of altemating current and to connect the output sides of said regulators in parallel across the common load. In the case of voltage regulators of the type in which the load current drawn from said regulators controls the operation thereof to maintain the output voltage of the system substantially constant, the load current output voltage characteristic thereof is usually rising 50 through at least a part of said characteristic.

Thus, for example, curves 1: and b of Fig. 2

might represent the characteristic curves respectively of two voltage regulators. In Fig. 2 the horizontal axis represents values of load current 55 while the vertical axis represents values of load characteristic a would be operating at P.

voltage. If we assume that the two voltage regulators are substantially of equal power rating and said two voltage regulators were connected in parallel, it would be desirable to divide any load drawn from said voltage regulators substantially 5 equal. Thus, for example, if it were desired to supply a value of load current such as that represented by L, each of the voltage regulators should furnish to the load a value of current represented by M. Under these conditions the 10 regulator having the characteristic b would be operating at P, and the regulator having the Since under these conditions the point P is at a higher voltage than point P, the voltage regulator with the characteristic b would tend to force a larger amount of current through the load. As the current from said voltage regulator increased. the output voltage thereof would rise due to the rise of the characteristic curve b, and therefore the m tendency for said regulator to supply an additional amount of current to the load would be increased. This condition would cause said voltage regulator to supply substantially all of the current to the load, and its operating point would move along to point Q on the characteristic curve b while the voltage regulator having the characteristic curve a would cease to supply current to the load and its output current would drop substantially to zero. In Fig. 2 I have represented the two voltage regulators as having slightly different characteristics. However, evenin the case of identical characteristics, the same type of operation would almost inevitably occur. If two such identical regulators were operating on a rising portion of their characteristics, a slight disturbance in the system, causing one of said regulators to supply a slightly increased current to the load, would upset any conditions of equilibrium which might have existed and cause that regulator to supply an increasingly larger proportion of the load until its operation had shifted to such a point where it supplied substantially all of the current to the load, while the other voltage regulator would cease supplying any substantial amount of current to said load.

I have found that the above difllculty may be eliminated by connecting voltage regulators in parallel in accordance with my invention. In Fig. 1;.which represents one form of said inventlon, I have illustrated two voltage regulators I and 2 adapted to be connected in parallel across a common supply of alternating current and supplying in parallel a common load I. The dotted line through the central portion of Fig. 1 is used to designate the separation between the two voltage regulators I and 2. Each of said voltage regulators consists of a rectifier 4 fed from a secondary winding 5 of a transformer 6 whose primary winding I has in series therewith inductance coils 8 and 9 of a control choke I0. The two inductancecoils 8 and 9 are preferably connected in parallel to secure such operation as is more fully set forth in the co-pending application of Frederick S. Dellenbaugh, Jr., Serial No. 759,852, filed December 31, 1934. The rectifier 4 is illustrated diagrammatically as being a fullwave rectifying bridge. Any other rectifying arrangement could be used, such as for example a full-wave rectifying tube or tubes or even a single-wave rectifier. The choke Ill consists preferably of a three-legged core ll having the coils 8 and 9 wound on the two outer legs I2 and I3 thereof. Two additional coils I4 and I5 are also wound on the legs l2 and I3, and connected in series with each other. The coils 8, 9, I4 and I5 are so related that any alternating current induced in coil I4- is neutralized by a substantially equal and opposite alternating voltage induced in coil I5. The rectifier 4 has two output terminals I6 and H. One of the output terminals, for example I7, is connected by a conductor I8 through coils I5 and I4 and then by an additional conductor l9 to an input terminal of a filter 2|. The other output terminal is of the rectifier 4 is connected by a conductor 22 to the other input terminal 23 of the filter 2|. The two output terminals 24 and 25 of filter 2I of the voltage regulator I are connected by conductors 26 and 21 to input terminals 28 and 29 of load 3. The two output terminals 24 and 25 of filter 2| of regulator 2 are likewise connected by conductors 30 and 3| to the conductors 26 and 21, respectively, whereby the output of regulator 2 is connected in parallel with the output of regulator I across the common load 3. The system may be provided with two input terminals 32 and 33 which are adapted to be connected -to some suitable source of alternating current. One of the input terminals, for example terminal 32, is connected by means of a conductor 33' to the coils 8 and 9 of regulator I. An additional conductor 34 connected to the conductor 33' is connected to the two coils 8 and 9 of the regulator 2, thus connecting said coils to the input terminal 32. The coils B and 9 of regulators I and 2 are each connected by means of an additional conductor 35 to one end of the primary winding I of transformer 6. The other end of the primary winding 1 of regulator I is connected by means of a conductor 36 to the other input terminal 33, and likewise the other end of primary winding 1 of regulator 2 is connected by a conductor 3'! to said other input terminal 33. Instead of coils 8 and 9 being in parallel, it is sometimes desirable to connect these coils in series with each other. The terminals of the secondary winding 5 of each voltage regulator are connected to two input terminals 38 and 39 of the rectifier 4.

When an alternating voltage is applied to the input terminals 32 and 33 and a direct current load is drawn from the load terminals, the load current will divide between the two voltage regulators and current will flow through the various coils shown. The current so flowing will introduce voltage drops in these various coils, and will also introduce voltage drops in each rectifier 4 and in each filter 2| associated therewith. By passing the load current drawn from each recti fier through the coils I4 and I5, this load current will tend to saturate the core II and thus reduce the reactance of coils 8 and 9. This reduction in the reactance or inductance of these coils will decrease the voltage drop introduced by these coils, and will permit a larger portion of the impressed. voltage to be impressed upon each primary 1. This causes the voltage across each secondary 5, which voltage is impressed upon the respective rectifiers 4-, to increase with an increase in load. By properly designing the various constants of the system, this increase in voltage can be made to compensate for the additional voltage drops, due to the increase in current through the system, and produce for each voltage regulator such a substantially constant voltage current output curve as might be illustrated diagrammatically by characteristic curves a and b of Fig. 2.

As has been pointed out above, if such a system as I have described contained no additional means than those described above for preventing a non-desirable division of current between the two regulators, the current supplied to the load would not be supplied by each regulator in the desired manner, and the difficulties set forth would result. I have found that by providing an equalizing connection 40 substantially in the manner as shown in Fig. 1, these difficulties are avoided. This equalizing connection 49 is connected between the equalizer terminals 4! and 42 of the regulators I and 2, respectively. The equalizer terminal 4| is connected by a conductor 43 to the output terminal I! of the rectifier 4 of regulator i. The equalizer terminal 42 is connected by means of a conductor 44- to the output terminal I! of rectifier 4 of regulator 2.

I have also found that it is desirable for each filter 2| to be so constructed that between the input terminal 23 and the output terminal 25 be provided a connection 45 in which is interposed substantially no impedance. The various choke members of the filter 2| may be connected in the other side of the filter as illustrated diagrammatically by the dotted choke 46, while the various condenser elements, such as represented by dotted condensers 41, may be connected between the two sides of said filter. The dotted members 46 and 41 are merely intended to represent possibly a more complex arrangement of a plurality of such members. Due to this arrangement it will be seen that the output terminals of both rectifiers 4 are connected directly in parallel with each other on one side by the conductors 40, 43 and 44, and on the other side by the conductors 22, 45 and 3|. Thus the voltage at the output terminals of each rectifier 4 must be the same as the voltage at the output terminals of the other rectifier at all times. In certain circumstances, such as where regulators of equal power rating are used, it might be useful to interconnect the input terminals of the rectifiers of like polarity. Such a mode of connection, while not as effective as the connection illustrated in Fig. 1, will prevent an excessive inequality of load division. In a broad sense, however, the connection 49 can be considered as being from a point intermediate the output terminals of the secondary winding 5 and the coils l4 and IS on each regulator to a similar point on the other regulator. In order to explain the principles of my invention and to illustrate why such an equalizer connection 40 connected in the manner illustrated accomplishes the desired results, I have schemataooaasr ically represented in Fig. 3 substantially the equivalent circuit of the arrangement as shown in Fig. 1. The reactance of coils I and S of regulator l is represented by in. The effective reactance of the transformer 6 of regulator-i referred to the primary circuit thereof is represented by X1. The reactance of coils I and 8 of regulator 2 is represented by K1. 'Ihe effective reactance of the transformer 8 of regulator 2 referred to the primary circuit thereof is represented by X. The effective resistance of the filter 2| of regulator i as referred to the primary of transformer thereof is represented by Rs. The eilective resistance of the filter 2| of regulator 2 as referred to the primary I thereof is represented by R1. The effective resistance of the load referred to the primary system of the two voltage regulators is represented by Rs. Since the current which flows through the respective filters likewise controls the reactance of the coils I and i of the respective regulators, I have represented this fact in Fig. 3 by the dotted lines connecting the circuits in which Re and R1 are placed to the arrows representing adjustability of the two inductances X1 and 1%, respectively. The presence of the equalizer connection II in Fig. 1 eil'ectively introduces into the equivalent circuit of Fig. 3 the connection F in the position as indicated therein, the symbols I1. and II to Is, inclusive. together with their associated arrows, represent .the current flowing through the various parts of the system. Any other equivalent impedances of the circuit shown in Fig. l which might be represented in Fig. 3 are of such small value in a practical system that the effect upon the operation and analysis of that system may be neglected without substantially affecting that analysis.

The operation of the equivalent circuit as shown in Fig. 3 is analyzed vectorially in Fig. 4.

In the analysis as illustrated in Fig. 4, I have assumed that regulator I is designed for twice.

the power rating for which the regulator 2 is designed. This analysis will indicate the manner in which the current supplied to each voltage regulator is in proportion to its power rating. In Fig. 4 I have represented a condition of equilibrium and will point outsub'sequently wherein my system tends to maintain that condition of equilibrium in a stable manner.

The vector Er. in Fig. 4 represents the line voltage applied to the system. If a load currentis drawn through the load R5, a current In will be drawn from the line. Due to the presence of the relatively high inductance of the regulating system, this current In will lag behind the voltage EL, as indicated in Fig. 4. The voltage Er. may be divided into two components EA and En. Due to the fact that circuit A is substantially entirely inductive and circuit B has considerable resistance therein, there will be an angular displacement between the two voltages EA and En. The current In flowing into the circuit A will subdivide into currents I1 and I3. Since the same voltage EA is impressed across the two inductances X1 and X:, the currents I: and I; will be inversely proportional to the value of said inductances, respectively. In voltage regulators such as I have illustrated, the inductances X1 and X: will be inversely proportional to the power rating of the respective regulators. Thusifaregulator is built with a higher power rating than another regulator, its inductance Xi will be lower due to the presence of the larger amount of material which is used and the higher values of current which it is designed to handle. Thus the currents I1 and I: will be related to each other substantially in accordance with the power rating of the respective regulators. If regulator I has twice the power rating of regulator 2, I1 will be twice I1, as-shown in Fig. 4. The voltage drop through the inductances Xi and m is entirely inductive, and therefore this voltage which is equal to Es occurs at right angles to the currents I; and I1. Also due to the fact that the two inductances X1 and K1 are substantially pure inductances, I1 and I: will be substantially in phase with one another, and therefore will add directly to give the resultant line current IL- As the current I1 reaches the circuit C, it will divide into the two currents I: and Is, and likewise the current 13 upon reaching the circuit D will divide into the currents I4 and I0. The inductances X: and X4 likewise are inversely proportional to the power rating of their respective regulators for substantially the same reasons as set forth with respect to the inductances X1 and X1. Since the same voltage Ea is impressed across both of these inductances X: and X4, the relationship between the two currents flowing through said inductances, namely I2 and I4. will be in inverse ratio to the values of said inductances X: and X4. Due to this condition, the currents I: and I4 will be related to each other substantially in accordance with the respective power rating of their regulators. Therefore if regulator i has double the power rating of regulator 2, I: will be double I4 as shown in Fig. 4. The two currents Ia and I4 will be at right angles to the voltage Es because of the fact that these currents flow through a purely inductive circuit. In order to determine the magnitude of the currents hand I, it is merely necessary to subtract from the currents I1 and I: the respective currents I: and I4. If this is done, it will be found that the resultant current Ia will be double the resultant current In. Since the network through which these two currents flow is entirely a resistance network, these currents will be in phase with the voltage En impressed across said network. Since Ia and I9 represent the load current supplied from the regulators l and 2, respectively, it will be seen that by the arrangement which I have illustrated, under a condition of equilibrium, the load current I5 will subdivide between the two regulators substantially in accordance with their power rating. Since the circuits in which Rs and R7 are placed are in parallel with each other, the same voltage will be impressed across them, and therefore the current I5 will divide between them inversely in accordance with the respective value of R6 and R7. R6 and R1 likewise will be related to each other substantially inversely in accordance with the power rating of their respective systems for substantially the same reasons as set forth with respect to X1 and X2. Therefore Is and I1 will be related to each other substantially in accordance with the power rating of their respective systems. Under the conditions which I have assumed, I6 will therefore be double I1. The vector sum of these two currents will likewise be I5. Under these conditions I6 and I1 will be substantially equal to I8 and I9, respectively. Thus under a condition of equilibrium, the regulating current for each voltage regulator will be substantially equal to the load currents applied by that voltage regulator, and thus the proper output characteristic of each regulator will be secured so as to maintain at the load a substantially constant voltage.

If instead of such a condition of equilibrium as I have assumed with respect to Fig. 4, there exists a temporary unbalance of conditions, currents will flow through the various parts of the system tending to re-establish the condition of equilibrium. Thus if two voltage regulators having the characteristics a and b, as illustrated in Fig. 2, are connected in parallel and it is desired to operate these regulators so that each supplies the current of the value M, temporarily a condition might be created in which an equilibrium did not exist. If we assume that regulator I has the characteristic b and regulator 2 has the characteristic a. in Fig. 3, the voltage across X2 would tend to be higher than the voltage across X4, and thus Ia would increase with respect to In, thus resulting in a decrease of 19. The load current I5 would, however, remain substantially constant. Since the division between Is and I1 does not depend upon the voltage conditions which exist across X2 and X1 but only upon the value of Is and the relative values of Re and R1, Is and 11 would still be related in accordance with the power rating of the respective regulators. Therefore these two currents I6 and 11 would remain substantially constant and there would not be any substantial change in the values of either X1 or X3. The increase in It and possibly an increase in I: would result in an increase of I1.

Likewise a decrease in I3 would be efiected. Since X1 would remain substantially constant, the increase in I1 would produce an increased drop through X1, and therefore would tend to decrease the voltage across X2. Likewise the de- 3 crease in the current I3 through the then constant reactance X3 would cause a decrease in the voltage drop across X1, and therefore would tend to increase the voltage across X4. Under such a condition of unequilibrium, the characteristic b at the point P, instead of tending to have a rising characteristic, would temporarily have a falling characteristic, and therefore the tendency to supply all of the load current, which would exist without the equalizing connection 40 or F, no longer is present. Upon reaching a point of equilibrium with regulators having the characteristic shown in Fig. 2, it will be found that Is will have increased slightly over the desired ideal distribution of current and I9 will have decreased slightly over such an ideal sufficiently to introduce an added voltage drop in X1 and slightly decrease the voltage drop in X3 sufficiently to make the voltages at points P and P1 equal to each other. Upon referring to Fig. 4

.; it will be seen that the voltage EA, which represents the inductive drop through the inductances X1 and IQ, is a fairly large proportion of the voltage EL. Under these conditions, a very slight change in the currents I1 and I3 is necessary to effect the proper corrective voltage drop to reach a condition of equilibrium, even with such dissimilar characteristics as illustrated in Fig. 2.

Thus upon reaching such a condition of equilibrium, the change in currents I8 and I9 will be so small that the relationship between them will still be substantially in accordance with the power rating of their respective regulators. Of course asv the characteristic curves of the systems connected in parallel more closely approximate each other, the smaller will be the deviation of the division of the load currents from the theoretical ideal. With any two systems connected as I have illustrated, the operation thereof is extremely stable and the division of the load currents between the systems, often under conditions of considerably diflerent voltage characteristics, is substantially in accordance with the power rating of the respective regulators.

or course it is to be understood that this invention is not limited to the particular details of the arrangement as described above as many equivalents will suggest themselves to those skilled in the art. For example, various circuit changes may be made which will produce substantially the same effect as the circuit arrangement shown in Fig. 1. Thus, if instead of using separate primary and secondary windings for the transformer, a single winding were used upon which primary and secondary circuit connections were'made, the operation of the system would be substantially the same. Therefore, when using the term connected across any element in the claims, I intend that this expression shall designate either an inductive coupling of two elements, such as primary and secondary windings 1 and 5, or a direct electrical connection across such an element. Likewise when using the expression connected in series to designate the connection between two elements or circuits I intend that this expression shall be broad enough to include an inductive coupling as part of said series connection, such as, for example, the primary and secondary windings l and 5 or a direct electrical connection of the two elements or circuits. Various other changes will likewise suggest themselves. It is accordingly desired that the appended claims be given a broad interpretation commensurate with the scope of the invention within the art.

What is claimed is:

1. A voltage regulating system comprising a plurality of voltage regulators each comprising impedance means adapted to be connected in series with a source of alternating voltage, a separate output circuit connected in series with each of said impedance means, and current-responsive means in each of said output circuits for varying the associated impedance means inversely in response to the amount of current flowing through the respective current-responsive means to produce a rising voltage output characteristic for its regulator, said output circuits being connected' in parallel across a common load, said current responsive means being connected in parallel with each other and in series with said common load.

2. A voltage regulating system comprising a plurality of voltage regulators each comprising two impedance means adapted to be connected in series with a source of alternating voltage, a separate output circuit connected across one of each of said pairs of impedance means, and ourrent-responsive means in each of said output circuits for varying the other impedance means of the associated pair of impedance means inversely in response to the amount of current flowing through the respective current-responsive means to produce a rising voltage output characteristic for its regulator, said output circuits being connected in parallel across a common load, said current-responsive means being connected in parallel with each other and in series with said common load.

3. A voltage regulating system comprising a plurality of voltage regulators each comprising two inductance means adapted to be connected in series with a source of alternating voltage, a separate output circuit connected across one of each of said pairs of inductance means, and current-responsive means in each of said output circuits for varying said other inductance means of the associated pair of inductance means inversely in response to the amount of current flowing through the respective current-responsive means to produce a rising voltage output characteristic for its regulator, said output circuits being connected in parallel across a common load, said current-responsive means being connected in parallel with each other and in series with said common load.

4. A voltage regulating system comprising a plurality of voltage regulators each comprising two impedance means adapted to be connected in series with a source of alternating voltage, rectifying means connected across one of said impedance means, said rectifying means having output terminals, an output circuit across said output terminals, and current-rwponsive means in said output circuit for varying said other impedance means inversely in response to the amount of current flowing through said current-responsive means to produce a rising voltage output characteristic for its regulator, said output circuits being connected in parallel across a common load, said current-responsive means being connected in parallel with each other and in series with said common load.

5. A voltage regulating system comprising a plurality of voltage regulators each comprising two inductance means adapted to be connected in series with a source of alternating voltage,

rectifying means connected across one of said inductance means, said rectifying means having output terminals, an output circuit across said output terminals, and current-responsive means in said output circuit for varying said other inductance means inversely in response to the amount of current flowing through said currentresponsive means to produce a rising voltage out put characteristic for its regulator, said output circuits being connected in parallel across a common load, said current-responsive means being connected in parallel with each other and in series with said common load.

6. A voltage regulating system comprising a plurality of voltage regulators each comprising inductance means in series with the primary circuit of a transformer, said transformer having a secondary circuit connected to rectifying means, said rectifying means having output terminals, an output circuit across said output terminals, and current-responsive means in said output circuit for varying said inductance means inversely in response to the amount of current flowing through said current-responsive means -to produce a rising voltage output characteristic for its regulator, said output circuits being connected in parallel across a common load, said current-responsive means being connected in parallel with each other and in series with said common load.

WILCOX P. OVERBECK. 

